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Old 09-02-2009, 06:25 PM   #1
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Foam insulation, or not!


I have a 100 year old house, wood framed with aluminum siding exterior and plaster w/lathing interior. I am thinking about installing a retrofoam product However, I understand the foam is permeable by water. Since common old construction is a hollow wall with no vapor barrier, I'm wondering if installing foam into the exterior walls would result in inside water vapor (or even outside water vapor) working its way into the foam and causing a mold problem. Any thoughts on this would be appreciated.

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Old 09-02-2009, 09:17 PM   #2
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Foam insulation, or not!


Not sure where you live but closed cell foam will be fine in any climate zone without a vapor barrier on either the inside or outside. Open cell should have a vapor barrier on the inside in Zone 6 or above. Painted drywall is suitable as an inside vapor barrior. (From Building Science.com). I absolutely agree foam is the way to go especially where it is difficult to air seal. The exterior walls of an old house would be very hard.

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Old 09-03-2009, 12:04 PM   #3
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Foam insulation, or not!


My understanding is that a closed cell foam is essentially a vapor barrier. If a closed cell foam is applied to the exterior of a house in a cold climate and the R value of the foam is insufficient then the inside surface of the foam can drop below the dew point temperature of the interior air that is migrating out of the house. This would cause condensation and potential rot problems. If the foam has a high enough R value then the inner surface of the foam will remain above the dew point and not lead to condensation.
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Old 09-03-2009, 05:50 PM   #4
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Foam insulation, or not!


The stuff they use is a nonexpanding open cell foam and therin lies my concern. thanks for your thoughts.
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Old 09-03-2009, 07:29 PM   #5
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Foam insulation, or not!


Basic: http://www.energysavers.gov/your_hom.../mytopic=11620

Advanced: http://www.healthgoods.com/Education...foam_board.htm

Best: http://www.buildingscience.com/docum...gs?full_view=1
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Old 09-04-2009, 12:39 PM   #6
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Foam insulation, or not!


what about blown in insulation, loose cellulous? that would save the horrendous mess of opening up lath & plaster walls.

Knucklez

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